Most vehicles are equipped with a cabin HVAC unit designed to transfer heat from the refrigerant and heated coolant into air, and to blow the air into the vehicle cabin. The HVAC unit may contain a heater core, an evaporator core, a plenum, and a plenum blower, among other components. The plenum may include various deflection doors and ducts that divert air to various vents disposed within the vehicle cabin. As doors within the plenum swing open or adjust, the air flowing through the plenum is distributed from one vent system to another. As the heated air travels through the heater and evaporator cores, water vapor in the air surrounding the cores may condense and collect in the bottom of the plenum. The plenum may include a drain tube used to drain the condensed liquid. At times, the drain tube may become clogged and rendered unable to drain the condensed liquid from the plenum.